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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HBASE-7051) CheckAndPut should properly read MVCC
Date Wed, 31 Oct 2012 22:03:15 GMT

     [ https://issues.apache.org/jira/browse/HBASE-7051?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Lars Hofhansl updated HBASE-7051:
---------------------------------

    Summary: CheckAndPut should properly read MVCC  (was: Read/Updates (increment,checkAndPut)
should properly read MVCC)
    
> CheckAndPut should properly read MVCC
> -------------------------------------
>
>                 Key: HBASE-7051
>                 URL: https://issues.apache.org/jira/browse/HBASE-7051
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 0.96.0
>            Reporter: Gregory Chanan
>            Assignee: Lars Hofhansl
>             Fix For: 0.94.3, 0.96.0
>
>         Attachments: 7051.txt
>
>
> See, for example:
> {code}
> // TODO: Use MVCC to make this set of increments atomic to reads
> {code}
> Here's an example of what I can happen (would probably be good to write up a test case
for each read/update):
> Concurrent update via increment and put.
> The put grabs the row lock first and updates the memstore, but releases the row lock
before the MVCC is advanced.  Then, the increment grabs the row lock and reads right away,
reading the old value and incrementing based on that.
> There are a few options here:
> 1) Waiting for the MVCC to advance for read/updates: the downside is that you have to
wait for updates on other rows.
> 2) Have an MVCC per-row (table configuration): this avoids the unnecessary contention
of 1)
> 3) Transform the read/updates to write-only with rollup on read..  E.g. an increment
 would just have the number of values to increment.

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